APPENDIX C: VLAN Application Note
Overview
A Virtual Local Area Network (VLAN) is a network topology configured according to a logical
scheme instead of the physical layout. It can be used to combine any collection of LAN segments
into a group that appears as a single LAN so as to logically segment the network into different
broadcast domains. All broadcast, multicast, and unknown packets entering the Switch on a
particular VLAN will only be forwarded to the stations or ports that are members of that VLAN.
Generally, end nodes that frequently communicate with each other are assigned to the same
VLAN, regardless of where they are physically on the network. In this way, the use of VLANs can
enhance performance by conserving bandwidth and improve security by limiting traffic to specific
domains. Another benefit of VLAN is that you can change the network topology without physically
moving stations or changing cable connections. Stations can be ‘moved’ to another VLAN and
thus communicate with its members and share its resources, simply by changing the port VLAN
settings from one VLAN to another VLAN. This allows VLAN to accommodate network moves,
changes and additions with the utmost flexibility.
The Managed Switch supports Port-based VLAN implementation and IEEE 802.1Q standard
tagging mechanism that enables the switch to differentiate frames based on a 12-bit VLAN ID (VID)
field. Besides, the Managed Switch also provides double tagging function. The IEEE 802.1Q
double tagging VLAN is also referred to Q-in-Q or VLAN stacking (IEEE 802.1ad). Its purpose is to
expand the 802.1Q VLAN space by tagging the inner tagged packets. In this way, a “double-
tagged” frame is created so as to separate customer traffic within a service provider network.
Moreover, the addition of double-tagged space increases the number of available VLAN tags
which allow service providers to use a single SP-VLAN (Service Provider VLAN) tag per customer
over the Metro Ethernet network.
While this application note can not cover all of the real-life applications that are possible on this
Managed Switch, it does provide the most common applications largely deployed in most
situations. In particular, this application note provides a couple of network examples to help users
implement Port-Based VLAN, Data VLAN, Management VLAN and Double-Tagged VLAN. Step-
by-step configuration instructions using CLI and Web Management on setting up these examples
are also explained. Examples described below include:
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